Low-order Streams Research Articles

Exploring methods of measuring CO2 degassing in headwater streams

Carbon dioxide (CO2) degassed from ungauged, headwater streams has a significant role in carbon cycling and climate change, making the precise measurement of the degassing of critical importance. Although methods exist for quantifying degassing rates in large bodies of water (seawater, lakes), these methods are often considered invalid for measuring degassing rates in small, turbulent, groundwater fed headwater streams. This manuscript reviews the physics of gas transfer across the stream-atmosphere interface and provides an in-depth critical review of the available methods of measuring CO2 degassing. Further, it discusses applications for some of these methods in small headwater streams and other low-order streams that are dominated by discharged groundwater. Of the methods reviewed, almost all produce fairly low precision and do not compare well with other methods tested in the same location. We suggest much more work is needed to improve the precision and accuracy of field-measured gas transfer coefficients, both by applying multiple methods in the field and by controlled laboratory experiments.

Effects of the Invasion of Honey Locust (Gleditsia triacanthos L.) on Macrophytes and Algae of Pampean Streams (Argentina)

Invasion by Gleditsia triacanthos L. (honey locust) along the banks of Pampean streams and rivers appears to induce profound changes in species richness, macrophyte cover, and producer biomass. Seasonal effects of the invasion on macrophytes cover and biomass of seston, periphyton, and benthos were studied at three low order streams from the Pampas region (name them here), in sections with and without invasion of honey locust. We hypothesized that light reduction by honey locusts reduces macrophyte coverage and algal biomass, thereby modifying the structure of the stream communities. Incident light and nutrient concentrations showed differences between invaded and not invaded reaches. Stream sections with tree canopy showed a negative correlation with the percentage of macrophyte cover (R = -0.41, p < 0.05). In the three streams, the biomass of seston, periphyton and benthos was reduced in summer, when canopy cover was most developed. This study demonstrates that a high degree of honey locust invasion modifies the structure of aquatic communities of Pampean streams therefore urgent action is needed. Options for honey locust management are suggested.

Resilience of benthic macroinvertebrates to extreme floods in a Catskill Mountain river, New York, USA: Implications for water quality monitoring and assessment

Abstract Changes in the timing, magnitude, frequency, and duration of extreme hydrologic events are becoming apparent and could disrupt species assemblages and stream ecosystems across the Northeastern United States. Between August 28 and 29 of 2011, an average of 31 cm of rain from Tropical Storm Irene fell across Eastern New York State in less than 24 h and caused historic flooding in numerous streams of the Catskill Mountain Region. Peak discharges exceeded the 0.01 annual exceedance probability (>100 year flood) in many Catskill Mountain streams. Approximately one week later, the remnants of Tropical Storm Lee deposited another 19 cm of rain onto saturated soils and caused additional flooding. Data from annual benthic macroinvertebrate surveys completed at 5 sites in the Upper Esopus Creek, a premier trout stream in the region, during August 2009–2011 (before the floods) were compared to data collected from the same sites in September 2011, November 2011, March 2012 and August 2012 (after the floods). The impact, rate of recovery and the factors which might affect the resilience of benthic macroinvertebrate communities were evaluated. The results of biological water quality assessment metrics immediately after the floods resembled those of highly polluted waters, yet severe floods were the only disturbance. Prior to the floods, standard biological assessment metrics showed that communities were not impacted and water quality was pristine. A large decrease in macroinvertebrate density was evident in the September 2011 surveys following the floods and bioassessment metrics reflected highly degraded water quality conditions. Most community metrics rebounded in 3–7 months (November 2011 and March 2012), and full recovery was evident in 12 months (August 2012) which suggests that macroinvertebrate assemblages are relatively resilient to the effects of extreme floods in these low-order streams. Therefore, macroinvertebrate samples collected from a flood-impacted stream before full recovery occurs might reflect loss of diversity and abundance from the flood disturbance and incorrectly attribute the impact to impaired water quality. The strong short-term impacts and the relatively rapid recovery of macroinvertebrate communities following catastrophic floods have important ramifications for routine bioassessment programs considering changing hydrologic regimes in streams across the Northeast and elsewhere.

Using stable isotopes and tritium to delineate groundwater flow systems and their relationship to streams in the Geum River basin, Korea

This study aims to clarify groundwater and stream water flow systems in the Geum River basin, Korea, which is an area with a crystalline basement using δ18O, δ2H, and 3H. Stable isotopes of precipitation showed clear differences between dry and rainy seasons due to the Asian monsoon. Groundwater and stream water samples were collected in the dry and rainy seasons in three hydrographic zones of the upper, middle, and lower zones. The contribution of rainy season precipitation to groundwater recharge based on deuterium excess was 71–89%, far exceeding the amount fraction of the season in total precipitation. Stable isotopic compositions of groundwater and stream water showed little seasonal variation, and indicated the dominance of high-altitude recharge in the upper zone. Groundwater with lower 3H was mainly observed in that area, indicating a contribution of intermediate flow with a longer residence time. In contrast, stream water and some groundwater samples in the lower zone showed seasonal variability and signatures of 10–20% evaporation in their stable isotopic composition. The 3H content of groundwater in the lower zone was high, indicating that the local flow system is dominant. These regional features also influenced the relative contributions of rainy season precipitation, dry season precipitation, and local recharge with evaporation signature, as estimated from δ18O and deuterium excess values, and 3H in groundwater. Stream water from lower-order streams of the river had stable isotopic compositions similar to those in the upper zone, indicating a considerable contribution of groundwater discharge in the mountainous areas to the lower reach of the river. These results have implications for sustainable management of water resources in the basin during predicted changes in water usage and precipitation patterns due to climate change, as well as in regions with similar climatic and hydrologic conditions.

Using stable isotope approach to quantify pond dam impacts on isotopic niches and assimilation of resources by invertebrates in temporary streams: a case study

Fishponds built across streams can greatly affect their functioning, especially through loss of ecological continuity but also changes in water availability and trophic resources. Yet, their consequences on communities and stream functioning remain largely understudied. We investigated effects of fishpond dams on the trophic ecology of macroinvertebrate communities in temporary low-order streams using C and N stable isotopes. Food resources and macroinvertebrates were sampled in one upstream and one downstream site of two temporary streams, one stream without (reference stream) versus one with a fishpond (impacted stream) and used for isotopic analyses. Results suggested moderate effects of fishponds on the upstream tributaries. In contrast, at the downstream impacted site, ten times higher macroinvertebrate biomass and modifications in the trophic niches were recorded, likely due to changes in resource availability/quality and dam-related hydrology. By modifying the food sources as well as water fluxes, fishpond dams tend to alter macroinvertebrate communities but also shift the trophic dynamics downstream. This assessment stresses the need for exploring their impacts on food webs and nutrient fluxes at larger downstream distances to better understand their effects before drawing conclusions in regard to their management.

All change at the water\u2019s edge: invasion by non-native riparian plants negatively impacts terrestrial invertebrates

Riparian zones are complex, dynamic habitats that play a critical role in river ecosystem functioning. Terrestrial invertebrates comprise much of the diversity found in riparian habitats and facilitate the transfer of energy between aquatic and terrestrial systems. However, the consequences for terrestrial invertebrates of invasion of riparian zones by invasive non-native plants (INNP) remain poorly understood. Responses of terrestrial macroinvertebrate morphospecies to invasion by two common INNP, Fallopia japonica (Japanese knotweed) and Impatiens glandulifera (Himalayan balsam) were assessed, relative to local environmental factors. Terrestrial invertebrates were collected from 20 sites on low order streams in June and August alongside data on physical attributes and land use. Greater cover of F. japonica and I. glandulifera cover reduced total invertebrate abundance and morphospecies diversity at the individual sample scale, whilst increasing spatial heterogeneity of invertebrates at the site scale. Impatiens glandulifera reduced morphospecies diversity at the site scale with increasing cover, but this was not observed for F. japonica. INNP affected terrestrial invertebrate morphospecies abundance and diversity, to a greater extent than prevailing environmental conditions. Our findings therefore offer support for managing riparian plant invasions to improve habitat heterogeneity, restore terrestrial invertebrate diversity and repair aquatic-terrestrial linkages.

Influence of two neotropical ecoregions in the community of benthic macroinvertebrates

ABSTRACT This study aimed to investigate the differences of the macroinvertebrate community in two neotropical ecoregions. In this regard were sampled in 12 low-order streams, biological samples (benthic macroinvertebrates), water samples to determine physical and chemical characteristics (pH, dissolved oxygen, altitude, water temperature, alkalinity, water hardness, total nitrogen and total phosphorus) and was evaluated of the substrate in the riverbed. To compare attributes between the two ecoregions, was used the ANOVA and for the analysis of the structure and its relation with the physiographic parameters, the data were summarized by Principal Component Analysis. In addition, were classified the functional groups and indicator groups for each ecoregion. There were no differences between the ecoregions for attributes, however, the structure was different according to the PCA. Functional groups had different percentages for each ecoregion. The indicator taxa for Ecoregion ‘A’ were Baetidae, Aeshnidae, Coenagrionidae, Chironomidae and Ceratopogonidae and for Ecoregion ‘B’, the indicator taxa were Leptohyphidae, Caenidae, Perlidae, Pleidae and Psephenidae. The presence of the sensible indicator taxa infers that Ecoregion ‘B’ shows better habitat condition, It is due to the structural difference in substrate types, alkalinity, dissolved oxigen and water temperature.

Assessing effects of confined animal production systems on water quality, ecological integrity, and macroinvertebrates at small piedmont streams (Patagonia, Argentina)

Breeding of livestock in confined areas has recently become an alternative of production for farmers in Northwest Patagonia. Strong concern about how these practices can alter health and integrity of streams exists and mitigation measures from livestock impact have been recently incorporated to the legislation. We examined changes in water quality, riparian integrity, habitat conditions, and macroinvertebrates community at three low order streams having different modalities of animal production management. The general design included visits at 11 sites (comprising references sites) in a bimonthly scheme. We assessed hydrological and physicochemical features including oxygen, conductivity, nutrients and total suspended solids. Epilithic chlorophyll and bacteria (total coliforms and E. coli) were also measured. Integrity of each site was assessed by two adapted indexes for Patagonian streams: riparian ecosystem quality (QBRp) and habitat condition (HA). A suite of 12 qualitative bioindicator measures based on aquatic macroinvertebrates were utilized at two flow contrasting periods. Compared to reference sites, intensive and semi-intensive practices produced low to moderate impact regarding to oxygen saturation, conductivity and nutrient levels, but strong alteration of the riparian ecosystem and of the in-stream habitat condition were detected. E. coli counting resulted in declining of water quality at both intensive and semi-intensive management, and exceeded the recommended critical value for recreational purposes. Plecoptera and Trichoptera richness significantly diminished at most impacted sites during low water period. In addition, several macroinvertebrate metrics displayed negative and significant responses to ammonia level increases, evidencing a possible toxicity effect. Our findings suggest that these emergent practices, which are rapidly expanding in a relatively undeveloped area, might have negative impacts. Mitigation measures for stream protection should be recommended to landowners through conservation programs.

Modeling the Natural Drainage Network of the Grand River in Southern Ontario: Agriculture May Increase Total Channel Length of Low-Order Streams

The Grand River watershed is an important agricultural area in southern Ontario, with several large and growing municipalities. Based on digital elevation models (DEMs), the natural drainage network was modelled to predict flow paths. Channel lengths and locations of the predicted network were compared with a ground-truthed channel network to determine efficacy of the models. Approximately 5% of predicted channels lay &gt;40 m from actual channel locations. This amounted to 388 km of channel that had no corresponding channels in reality. The model was unable to predict, based on topography, 2535 km of actual channel present in the watershed. Channels not anticipated by topography were mostly first-order, with low sinuosity, were most common in areas with high agricultural land use, and are likely excavated extensions to headwater streams to facilitate drainage. In addition, this study showed that Soil and Water Assessment Tool (SWAT) models produced using different DEM resolutions did not predict significantly different stream flows, even when resolution was as low as 200 m. However, these low resolution DEMs did result in under-prediction of sediment export entering Lake Erie, most likely because the low resolution maps failed to account for small localized areas of high slope that would have relatively higher rates of erosion.

Geomorphic evolution of the Dongar River Basin, Son Valley, Central India

ABSTRACTThe present study is an attempt to describe the geomorphic evolution of the Dongar River Basin, Son Valley, Central India. To achieve this target, a detailed field survey and morphometric analysis of the river have been carried out using Cartosat-DEM data with the help of ArcGIS 10 software. The basin area of the Dongar River is 35.17 km2 having trellis and sub-dendritic to dendritic drainage patterns. The Dongar River is designated as fourth-order basin and lower order streams mostly dominate in the basin with the drainage density value of 1.21 km−1. The stream order of the basin is predominantly controlled by physiographic and tectonic set-up of the study area. The slope of basin varies from 0° to 42.04° and is mainly controlled by the local geology and erosional cycles. The bifurcation ratio (Rb) for the studied basin varies from 1.58 to 4. The higher values of the bifurcation ratio, i.e., of second/third along with third/fourth order, reveal the regional geological and tectonic controls when river starts draining along the exposures of lower Vindhyan . The elongation ratio of the basin is 0.86 thus indicates high infiltration capacity, low runoff, and low-to-moderate slope of the river basin. The increase in stream length ratio from lower to higher order shows that the basin has reached mature geomorphic stage. The major trends of lineaments are ENE – WSW, i.e., almost analogous to Son-Narmada lineament suggesting that Son-Narmada lineament played an important role to control the drainage dynamics and evolution of the adjacent river basins. These features along the Dongar River and the orientation of the major lineaments suggest neotectonics, may be due to reactivation of the Son-Narmada lineament.

Quantitative analysis of the drainage and morphometric characteristics of the Palar River basin, Southern Peninsular India; using bAd calculator (bearing azimuth and drainage) and GIS

ABSTRACTThe Palar River basin is one of the major rivers in southern peninsular India. Morphometric analysis coupled with drainage network analysis was carried out for the Palar River basin to understand its drainage characteristics and the drainage network geometry with reference to tectonics. The morphometric analysis has been carried out using ‘bearing azimuth and drainage (bAd) calculator’ which a new and easy methodology for extraction of watershed morphometric parameters. The entire Palar River basin has been divided into five major sub-basins and various linear, areal, and relief morphometric parameters were calculated. The sub-basins I, II, and III reflect low to medium stream frequency (Fs) and moderate drainage density (Dd) and a high bifurcation ratio of various stream orders signifies that they are surging through tectonically active areas, followed by high overland flow and less recharge into the subsurface resulting in low groundwater potential. Moreover, sub-basins IV and V show the relatively low overland flow, which helps to percolate water, hence ground water potential will be higher. The morphometric result suggests that the drainage network geometry is variously controlled by recent tectonics. Lineaments trending majorly NW-SE, NE-SW, and E-W mark the major drainage network in Palar River drainage basin. Lower order streams and higher order streams follow NW-SE, NE-SW lineaments. Which also points toward the tectonic control of drainage in Palar River. As a result of channel orientation due to tectonic activity: (i) most channels are A-type or B-type associated with the lineaments, (ii) the pattern of the drainage network is dendritic, rectangular sometime trellis too, and (iii) the main rivers flow longitudinally to the predominant lineament direction.

Grazers superimpose humidity effect on stream biofilm resistance and resilience to dry-rewet stress

Temperate low order streams increasingly experience intermittency and drying due to climate change. In comparison to well-studied Mediterranean streams, drying events in canopied temperate streams occur under higher ambient humidity which probably affects the metabolic response to drying. Previous work on drying sediments (in temperate streams) did not consider the interactions of trophic levels. We hypothesized that preservation of sediment moisture due to high humidity increases resistance to drying in temperate streambed biofilms and fast resilience of biofilm activity after flow resumption. We also expected the presence of macroinvertebrate grazers to modulate the biofilm response to dry-rewet stress. Following a two-level factorial design in 24 microcosms, we tested the effect of drying intensity (moderate and intense) and grazer presence and absence (P. antipodarum) on the activity of biofilm colonizing shallow hyporheic sediment. We measured the community respiration over a drying period of 27 days, a single rewetting event and a follow-up of three days. Grazer presence stimulated biofilm community respiration (CRmic) in the permanently wet control, but decreased biofilm resistance to desiccation (<0.2% of pre-disturbed activity), regardless of drying intensity. In the absence of grazers, higher atmospheric humidity in moderately drying microcosms resulted in maintaining a film of adhesive water and low CRmic (29% of pre-disturbed respiration) until the end of the drying period. After flow resumption, the CRmic increased within 8 h, achieving 79–83% of pre-disturbed respiration (no grazers) and 15–41% (with grazers), respectively. Results show that short dry periods in temperate streams, even under high humidity, impact the streambed biofilm community negatively. The complex response and strong effect of grazer presence indicates that experiments including interactions of trophic levels and settings mimicking environmental factors during dry-rewet stress are needed.

Stream invertebrate diversity reduces with invasion of river banks by non‐native plants

Abstract Invasion of riparian zones by non‐native plants is a global issue and commonly perceived as a challenge for river and fishery managers, but the type and extent of ecological changes induced by such invasions remain poorly understood. Established effects on sediment delivery, allochthonous inputs, and channel shading could potentially alter aquatic macroinvertebrate assemblages, with implications for in‐stream ecological quality. We assessed responses in the diversity, quality, and heterogeneity of stream macroinvertebrate communities to riparian invasion by non‐native plants. Macroinvertebrates were collected from 24 sites on low order streams in central and southern Scotland during spring and autumn. The effect of invasive non‐native plants (INNP) on macroinvertebrates was assessed relative to that of local physical and chemical factors. Invasive non‐native plants cover was associated with stronger effects than other factors on local diversity of macroinvertebrates (33% reduction at the highest INNP cover) but also increased macroinvertebrate abundance across sites. Invaded sites were also associated with lower macroinvertebrate biomonitoring scores. Community composition differed between invaded and uninvaded sites in autumn, but not in spring. However, INNP influence on macroinvertebrate composition was generally secondary to that of physicochemical variables (e.g. channel shade, substrate diversity). We demonstrate that the influence of INNP extends beyond well‐known impacts on plant communities to reductions mainly in stream macroinvertebrate diversity. Combined with the negative impact on pollution‐sensitive macroinvertebrate taxa this raises concerns over the ecological health of streams with heavily invaded riparian zones. Our findings suggest that efforts to improve low order streams by actively managing severe riparian invasions are merited, but the size and uncertainty of the likely ecological gains must also be evaluated against the effort involved.

DNA barcoding of fish fauna from low order streams of Tapajós River basin.

The Amazon basin harbors a megadiverse fish fauna spread in an intricate network of big rivers and small streams. The Amazonian streams are home of many small sized fishes that remains poorly documented. In order to accelerate the scientific knowledge on these important aquatic systems we adopted a modern integrative approach joining morphology and molecular tools to investigate the ichthyofauna assemblages from low order streams situated on the lower Tapajós River Basin. Cytochrome c Oxidase I (COI) DNA barcodes from 252 specimens collected from 10 stream sites were obtained. The combined analysis revealed 29 species, 21 genera and 11 families. Cryptic diversity was evidenced in Knodus sp.1, Aequidens epae and Copella callolepis, in which deep genetic divergence were detected (intraspecific distances: 20.48%, 7.99% and 3.77%, respectively). The putative new species showed closer relationships with their counterparts occurring in the Tapajós-Xingu water drainages.

&lt;b&gt;Does riparian vegetation affect fish assemblage? A longitudinal gradient analysis in three Amazonian streams

The degradation of riparian vegetation in low-order streams can cause irreversible environmental damage, biodiversity loss and alter the structure of communities. In this context, the present study evaluated how the level of degradation of riparian vegetation influences the fish assemblage in three low-order streams in the Brazilian Amazon. In each stream, three different stretches were delimited, distributed in the environments of forest, edge and pasture, and the samplings were conducted in three hydrological regimes using dip nets. Influences of the stretches and streams on richness and abundance were tested with GLMM, on the composition with PERMANOVA and on indicator species with IndVal. Species richness was higher in forest environments and lower in pasture; while abundance was higher in pasture and lower in forest. Species composition differed between stretches, streams and in the interaction between stretches and streams, with a strong difference between stretches of forest and pasture environments. Six species dependent of the riparian vegetation were classified as indicators of forest environments; while a generalist species was indicator of pasture. These results reinforce the negative influence of riparian vegetation removal on biological communities and provide subsidies that can help in the conservation and management of these systems.

Use of Lower-Order and Higher–Order Streams in Modelling the Rating Curve

The discharge of a lower-order stream empties into a higher-order stream. The higher-order flow is therefore influenced by the lower-order flow and this may be useful in predicting discharge in the tributary stream. The study is focused on fitting composite rating curve to stage of the higher-order stream and discharge of the lower-order stream. Available 1985 to 1988 stage and discharge data of Rivers Otamiri (higher-order stream) and Oramiriukwa (lower-order tributary stream) in Imo state, Nigeria, were used in the study. Curves are fitted to the data and the error of estimate, the coefficient of determination, R2% and F-test were used to judge the overall significance of the fitted models. The study revealed that the quadratic and power curves are clearly good representatives of the stage-discharge relationship in Otamiri River. The polynomial curve slightly represents the data better than the power curve in the case of Oramiriukwa River. It was revealed that Otamiri River was not in regime between 1985 and 1986. Only 1988 rating curve can be used to estimate flow in the river. The composite rating curve has a cubic function, S = 0.187Q + 0.027Q2 + 0.002Q3+0.726, in 1987 that best represents the stage-discharge relationship. This is because the correlation analysis indicates a 0.999 positive correlation coefficient and 99.9% of explained variance at the least standard error of 0.005. The statistical analysis demonstrate that the proposed methodology can be confidently used for rating curve development and discharge estimation at other (ungauged) sites, thus avoiding the manual discharge measurement at any river site not subjected to backwater effects.

Effects of shading on stream ecosystem metabolism and water temperature in an agriculturally influenced stream in central Wisconsin, USA

Headwater streams with a forested riparian zone and canopy cover have regulated stream temperatures and stream ecosystem metabolism because of shading. Agricultural practices have dramatically altered riparian corridors with the removal of mature vegetation, which consequently alters natural stream processes. The objective of this study was to investigate the effects of shading on stream temperature and ecosystem metabolism in an agriculturally influenced, low order stream. We examined three stream reaches; two in a recently restored stream (Lost Creek) and one in a nearby-unimpacted reference stream (Little Plover River). The two reaches in Lost Creek included a 100-m artificially-shaded stream reach and a control reach immediately upstream of the shaded reach. The Little Plover River included one reference reach with a fully forested canopy. Both streams are located in agricultural watersheds and based on phosphorus levels would be classified as meso-eutrophic. Each stream reach was assessed during stable flow conditions once each month between June and October of 2016. Rates of gross primary production (GPP), ecosystem respiration (ER), and net ecosystem production (NEP) were determined using the open system, two-station diel dissolved oxygen change method, and reaeration (k) was calculated using the nighttime regression method. Based on stream discharge data, we corrected metabolism values for groundwater when inputs exceeded 7% (Hall and Tank 2005). We also measured water temperature, PAR (photosynthetically active radiation), soluble reactive phosphorus (SRP), periphytic chlorophyll a content, and organic matter content at each site as potential controlling variables. Surprisingly, no significant differences were observed in daily maximum water temperatures among the three sites; however, GPP levels were significantly lower (ANOVA F2,14 = 45.45; p < 0.001) in the artificially shaded reach and the reference site compared to the control indicating that shading reduced GPP. ER was not significantly different among the reaches and remained relatively low, which resulted in the control reach having a highly positive and significantly higher NEP (ANOVA F2,14 = 17.656 p < 0.001) compared to the shaded and reference reaches. Redundancy analysis revealed that GPP and NEP were strongly correlated with PAR. Our findings suggest that shading can improve dissolved oxygen dynamics in an agriculturally-influenced stream by lowering GPP.

STREAMS DO WORK: MEASURING THE WORK OF LOW-ORDER STREAMS ON THE LANDSCAPE USING POINT CLOUDS

Abstract. The mutable nature of low-order streams makes regular updating of surface water maps necessary for accurate representation. Low-order streams make up roughly half the streams in the conterminous United States by length, and small inaccuracies in stream head location can result in significant error in stream reach, order, and density. Reliable maps of stream features are vital for hydrologic modeling, ecosystem research, and boundary monitoring. High resolution digital elevation models derived from lidar data have shown promise in low order stream modeling yet forested high relief landscapes and low relief agricultural areas remain challenging. Here we present early results from research analyzing lidar point clouds to identify features and patterns that may be used in low-order stream identification and classification in challenging geographic conditions. This work has identified characteristics derived from point clouds that correlate with the presence of streams and stream heads and show promise for mapping small streams. In low topographic relief agricultural areas, cross sections collected at regular intervals along drainage channels extracted as 3D lines show a significant jump in value and variance of profile curvature standard deviation at stream heads. In high relief areas, observations show potential for stream mapping by identifying trends in riparian zone structure. Lidar return point density from riparian vegetation under 30 feet tall dips in the vicinity of intermittent stream heads. Also seen is an increase in point density above 60 feet downstream of stream heads. The trends found here likely reflect a change in vegetation structure relative to the presence of streams.

Escherichia coli Concentration as a Function of Stream Order and Watershed Size.

This research examines the relationship of concentrations to stream order and watershed size and considers the implications on water quality standards. To assess geospatial effects, data were obtained from 743 monitoring stations in the Central Great Plains, Cross Timbers, and South Central Plains ecoregions of Texas and Oklahoma. Median and geometric mean concentrations were analyzed for correlation with stream order and watershed size at each site. Comparison of the three ecoregions revealed concentrations were highest in the westernmost Central Great Plains and lowest in the easternmost South Central Plains. Similarly, the strength of 's correlation with stream order and watershed area decreased with ecoregion moving west to east. Thus, incorporating ecoregion approaches when defining stream water quality standards is supported. Analysis showed no significant relationship of stream order or watershed size to concentrations in least-impacted watersheds (i.e., watersheds with minimal wastewater discharge and urbanization). Conversely, analysis of data from all sites showed a weak negative relationship between concentration and stream order and watershed size, with concentration generally decreasing with increasing stream order and watershed size. However, variability in smaller watersheds and lower-order streams supports continued use of site-specific studies to determine appropriate standards. Three-parameter exponential models provided an approach to estimate concentrations using Shreve stream order and watershed area and identify outlier streams potentially affected by anthropogenic activities where further investigation or remediation may be warranted.

Beaver Dams Induce Hyporheic and Biogeochemical Changes in Riparian Areas in a Mountain Peatland

Hyporheic exchange is important in increasing stream water transit time through basins and enhancing redox-sensitive biogeochemical reactions influencing downstream water quality. Such exchange may be enhanced by beaver dams which are common throughout low order streams including those originating in peatlands. To understand the influence of beaver dams on hyporheic flows and biogeochemical properties, nitrogen (N), dissolved organic nitrogen (DOC) and N cycling rates were observed along a beaver dammed, third-order stream draining Canadian Rocky Mountain peatland. Beaver dams enlarged the hyporheric zone from ≤1.5 to ≥7.5 m. The looping hyporheic flow path created a zone of N and DOC depletion adjacent to the dams. As a result, nitrification rates were lowest in this zone. Where hyporheic flows exited the riparian area and flowed back to the stream channel downstream of a dam, the adjacent riparian area served as a source of N and DOC to the stream. Enhanced nutrient influx to streams owing to beaver dam modified hyporheic flow paths has implications for stream biogeochemical cycling and ecological integrity, which need further exploration.